There is an urgent need for instrumentation that is capable of sustaining the development of rapid methods for the isolation, detection, and identification of traces of chemical and biological threat agents present in complex media. From anti-terrorist personnel, to first responders and law enforcement employees, police officers, airport screeners, and border patrol personnel, as well as members of the Navy, Army, Air Force, and National Guard, the risk of coming into contact with explosives and other weapons of mass destruction is high. Many of the samples collected for the forensic detection of explosives come from complex matrices that contain soil, dirt and other interfering substances. Additionally, soils can be contaminated with explosives by a number of different human activities, such as the use of explosives on training ranges, sites for the synthesis of explosives, as a result of conflicts between nations, from used waters and wastes in clandestine laboratories, and as a result of terrorist events, among others. Other common substrates that can be targets for the detection of explosives include debris, metals, plastics, woods, cardboard, fabrics, and so forth.
The majority of studies that have been published regarding the detection of explosives are based on spectroscopic and chromatographic methodologies, which obtain very low limits of detection. However, the use of chromatographic techniques in field applications has been very limited, primarily because of the lack of portable instrumentation. Conversely, many spectroscopic techniques have been successfully tested in field applications, facilitating the rapid acquisition of data and information, thereby leading to prompt decisions based on the obtained results and thus saving numerous lives and reducing casualties. Vibrational spectroscopy has been demonstrated to be valuable for the detection of high explosives, homemade explosives and toxic industrial compounds. In particular, infrared spectroscopy (IRS) has played a unique role in the detection of threat compounds. This technique has also been used for the post-blast detection of energetic materials using both globar and synchrotron infrared radiation sources, thus validating Fourier transform infrared (FT-IR) spectroscopy as a useful tool for forensic applications. The MIR spectral region consists of the spectral window from approximately 350 to 4000 cm−1. In this range, all molecules have characteristic vibrational signals that can be excited upon interaction with photons from the excitation source, thereby enabling the detection of trace amounts of compounds.
Thin layer chromatography (TLC) provides a streamlined sampling and testing protocol that allows for the rapid and reproducible separation of drugs, explosives and precursors, and pollutants, and its use can be extended to a wide range of hazardous materials obtained from substrates, liquids and solids for laboratory and field operations. The use of IRS as a detection/identification technique arises from the need to reliably identify the components separated by TLC. IRS has a high discrimination capability, and therefore, it is in principle a powerful identification method. Provided that reference spectra are available, almost all analytes, including structural isomers, can be nearly unambiguously identified based on their IR spectrum. Thus, the technique changes from a presumptive analysis (when TLC is used alone) to a confirmatory analysis when the separation technique is coupled with IRS. When reference spectra are unavailable, valuable information about the molecular structures of the analyzed compounds may still be obtained by spectral interpretation.
The majority of studies that have been published on the detection of explosives are based on spectroscopic and chromatographic methodologies, which obtain very low limits of detection. However, the use of chromatographic techniques in field applications has been very limited, primarily because of the lack of portable instrumentation. Conversely, spectroscopic techniques have the advantage of being tested in field applications, facilitating the rapid acquisition of data and information, thereby leading to prompt decisions based on the obtained results and thus saving numerous lives and reducing casualties. Vibrational spectroscopy has been demonstrated to be valuable for the detection of high explosives, homemade explosives and toxic industrial compounds. In particular, infrared spectroscopy (IRS) has played a unique role in the detection of threat compounds and has been used for the post-blast detection of energetic materials using both globar and synchrotron infrared radiation sources, thereby validating FT-IR spectroscopy as a useful tool for forensic applications. The MIR spectral region consists of the spectral window from approximately 350 to 4000 cm−1. In this range, all molecules have characteristic vibrational signals that can be excited upon interaction with photons from the excitation source, enabling the detection of trace amounts of compounds. TLC provides a streamlined sampling and testing protocol that allows for the rapid and reproducible separation and identification of drugs, explosives, and precursors, and its use has been extended to a wide range of hazardous materials obtained from surfaces, liquids and solids in laboratory and field operations. The use of IRS as a detection/identification technique arises from the need to reliably identify the components separated by TLC. IRS has a high discrimination capability and is therefore in principle a powerful identification method. If reference spectra are available, almost all analytes, including structural isomers, can nearly be unambiguously identified based on their IR spectrum. Thus, the TLC-IRS technique changes from a presumptive analysis (when TLC is used alone) to a confirmatory analysis when coupled with IRS. Valuable information about the molecular structures of the analyzed compounds may still be obtained by spectral interpretation when reference spectra are not available.
The first in situ FT-IR detection of spots on a plate was demonstrated by Percival and Griffiths. A thin layer (depth: 100 μm) of adsorbent on an IR transparent support (AgCl) allowed IR transmission measurements of dyes and amino acids at the 1-10 μg levels. In 1978, Fuller and Griffiths demonstrated the viability of diffuse reflectance IRS (DRIRS) in measurements of methylene blue on a silica plate. Since then, DRIRS has become the most commonly used method for performing in situ TLC detection with FT-IR. Several studies have been performed to explore the potential of TLC-DRIRS analysis. These studies, which have been extensively reviewed by Brown and Beauchemin, revealed that various conventional TLC phases, such as silica, alumina, cellulose and reversed-phase materials, can be used in combination with DRIRS to provide minimum identifiable quantities (identification limits) down to approximately 1 μg. The main difficulty encountered when using DRIRS as an in situ detection method for TLC is the strong absorption background of the adsorbent material, which causes serious interferences in particular spectral regions. For example, silica gel absorbs strongly in the regions from 3100 to 3700 cm−1 and from 1600 to 800 cm−1, obscuring possible analyte vibrational signals at these frequencies. Consequently, the DRIRS spectrum of a TLC spot is divided into main parts: spectral areas where the sensitivity is high and that are appropriate for obtaining analyte information and spectral regions where the signal-to-noise ratio is poor and only minimal information can be extracted.
The development of more powerful IR sources gave rise to collimated, coherent, and polarized sources. These sources were first developed at Bell Labs in 1994 with the invention of quantum cascade lasers (QCLs). QCLs are a commercially available and portable setup allowing the detection of chemical and biological threat compounds in the field, such as explosives including TATP, PENT, RDX, and TNT. Coupling with chromatographic techniques, such as TLC with QCL spectroscopy, for detecting explosives (or any chemical compound) has not been previously reported. The possibility of detecting explosives in the field more than justifies the coupling of TLC with QCL spectroscopy (QCLS).
TLC-QCLS, as a portable coupled technique for the analysis of explosives, will be most commonly used in two situations: (1) post-blast examination and (2) identification of suspected explosive materials (pre-blast analyses on bulk material). In a post-blast situation, preliminary results can lend support to the link between multiple incidents or between a terrorist incident and the organization potentially responsible for the incident. This portable coupled technique can provide critical information for the identification of a suspected explosive material. In these situations, portable instrumentation has a two-fold advantage: (1) the speed with which results can be obtained, and (2) eliminating the need to transport potentially dangerous materials to a laboratory. Identification at a scene enables informed decisions to be made concerning render-safe procedures and the transportation of materials. This is of particular importance when extremely sensitive explosives, such as organic peroxides, are suspected. When portable instruments are utilized during searches authorized by search warrants, the preliminary results can be used to indicate areas where more efforts should be directed. The preliminary results can also provide advanced warning about which types of explosives may be encountered at a scene and hence enable searchers to be better informed of the safety risks at a particular scene.
In this invention, a methodology that allows for the detection of explosives, such as TNT, present in real world samples (i.e., soils) and in complex substrates using TLC-QCLS is demonstrated. The tested methodology enabled the rapid and reproducible separation and identification of targeted explosives at near trace levels (˜ng) in the field in a short amount of time. The results show that TLC-QCLS, as a coupled technique, is an excellent approach to use in the lab or in chemical analyses in the field.
Throughout the figures, the same reference numbers and characters, unless otherwise stated, are used to denote like elements, components, portions or features of the illustrated embodiments. The subject invention will be described in detail in conjunction with the accompanying figures, in view of the illustrative embodiments.